Grids and known which have welding lines of top and bottom electrodes, which welding lines are arranged at a predetermined mutual distance apart in the longitudinal-wire advance direction and run transversely to the longitudinal-wire advance direction. A feeding apparatus feeds two cross wires along two insertion lines running transversely to the longitudinal-wire advance direction and arranged in front of the welding lines at their predetermined distance from one another. A transfer apparatus transfers the cross wires from the insertion lines into the welding lines, this apparatus having a plurality of supporting arms which are fastened to a common supporting beam, are provided with recesses for the cross wires, which recesses are arranged at a distance between the insertion lines. The arms and can be moved cyclically forwards and backwards in the longitudinal-wire advance direction by means of the supporting beam. A control device controls an operation in which one electrode row; and a control device via which one electrode row per welding line can be raised and lowered in cycles and the feeding and transfer apparatuses can be actuated.
Austrian Patent Specification 267,292, assigned to the assignee of this application, discloses a grid-welding machine of this type in which two cross wires are fed along insertion lines arranged in front of the welding lines and are advanced together with the longitudinal wires into the welding lines by means of a transport apparatus. The transport apparatus has a plurality of transport rails which are fastened to a common supporting beam and are provided with pairs of hooks for receiving the cross wires and with pairs of hooks, likewise acting on the cross wires, for simultaneously pulling the welded grid out of the welding lines. The distances between the hooks of each pair correspond to the desired cross-wire spacing in the finished grid, as a result of which this spacing is maintained very accurately and in an exactly reproducible manner. It has been found that the cross wires are deformed by the hooks at a higher production rate and that, in addition, the advance mechanism which is inevitably of particularly robust construction for a high production rate cannot guarantee the required rapid sequence of movement on due to an elevated moment of inertia.
EP-A-0,073,336, wenzel, discloses an advancing apparatus for longitudinal wires which is arranged in front of the welding line and consists of one transport drum each arranged above and below the longitudinal wires or of a plurality of transport-roller pairs per longitudinal wire. A gripping device arranged behind the welding line as viewed in the longitudinal-wire advance direction permits the advance of the grid when the residual lengths of the longitudinal wires have left the advancing apparatus described above. To push in the cross wires, transport drums or transport-roller pairs are actuated in cycles via a stepping control program, this program being corrected by means of a measuring instrument monitoring the longitudinal-wire advance. The apparatus has the disadvantage that complicated measuring and control devices are required for the advance of the longitudinal wires in order to avoid uneven advance, caused by varying wear of the transport drums or transport-roller pairs, and thus grid geometry.